In an electric generator, electricity is produced by a rotor spinning in a magnetic field. One way to produce the magnetic field is by using field coils with a current flowing in them. When there is no current in the coils, the magnetic field is not generated, and electric power is not produced by the generator. The process of generating a magnetic field by means of an electric current is called excitation.
By regulating the field current being fed into field coils of the generator, the generator terminal voltage can be controlled. Regulation of excitation and switching between excitation modes can be performed automatically. This can be done based on a status of a generator's breaker. When the status of the generator breaker is “open,” the excitation mode is “offline”; when the generator breaker is closed, the operation mode is switched to “online.”
However, a faulty status may be reported when a contact of the generator breaker malfunctions. If this is the case, the exciter is switched to a wrong operation mode, thus impairing the operation of the generator.